Control of Guest Thermal Release by Crystalline Host Orientation

Thermal release of guest molecules from poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films, exhibiting host–guest co-crystalline (CC) phases with orientation of their chain axes being preferentially parallel or perpendicular to the film plane (c // and c ⊥ orientations), is studied. TGA analyses show that, for all the considered CC PPO films, temperatures of guest release for CC films with c // orientation are definitely higher than those for CC films with c ⊥ orientation, with differences even higher than 100 °C. Correspondingly, DSC scans of CC films with c ⊥ orientation show separated endothermic peaks of guest release and melting, while CC films with c // orientation only exhibit one broad endothermic peak with superimposed guest release, glass transition ( T g ), and melting ( T m ) phenomena. This control of temperatures of guest release could be helpful to maximize the thermal stability of host–guest PPO co-crystalline phases and to tailor temperatures of active guest release.